Recently there has been considerable commercial success in the area of electronic devices having visual displays. Small hand held devices such as cell phones, PDA's, and mp3 players, and larger displays for television, signage and computers, depend to some extent on the appeal of their visual displays. Considerable work has been done trying to optimize such properties as brightness, color intensity, and power consumption in these displays. One active area of research is in effectively using organic light emitting diodes (OLEDs) and polymer light emitting diodes (PLEDs). Displays based on OLEDs and PLEDs offer substantial rewards in terms of being self-emitting (no need for back lighting), thinner, and lighter than more traditional illumination sources. However, because of the oxygen and moisture sensitivity of these classes of diode materials, the only currently generally suitable substrate material for OLED/PLED displays is glass.
Glass is used because of its superb water and oxygen barrier properties, and also because of its optical and mechanical stability. However, the art laments its lack of flexibility and the large minimum thickness in which glass can be provided. To replace glass, a plastic substrate would have to not only be flexible, but able to offer the properties of glass i.e. clarity, dimensional stability, thermal stability, barrier, solvent resistance, low coefficient of thermal expansion (CTE) coupled with a smooth surface. Currently no plastic films offer all these properties. Some plastic films come close to these required properties, e.g. polyester terephthalate (PET) and polyester naphalate (PEN), but they fall down with respect to thermal stability. Some of the processes involved in laying down organic light emitting and current conducting layers on the substrate are above the glass transition temperature of these polymers. Traditional manufacturing techniques would leave a polymeric substrate mechanically distorted by heat.